CN108395657B

CN108395657B - Self-repairing self-lubricating material and preparation method thereof

Info

Publication number: CN108395657B
Application number: CN201810040215.4A
Authority: CN
Inventors: 张琳; 解国新; 温诗铸; 雒建斌
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2018-01-16
Filing date: 2018-01-16
Publication date: 2020-08-21
Anticipated expiration: 2038-01-16
Also published as: CN108395657A

Abstract

The invention provides a self-repairing self-lubricating material and a preparation method thereof. The modified PTFE is a core/shell structure particle, the PTFE particle is used as a core, and the wear-resistant polymer or two-dimensional material is used as a shell; the microcapsule consists of a capsule core and a capsule wall, wherein the capsule wall is made of two-dimensional materials such as high polymer polymers such as urea resin, polyvinylpyrrolidone and the like or graphene, and the capsule core is a repairing agent such as dibutyl phthalate, glycidyl methacrylate, linseed oil and the like. The material improves the problems of poor compatibility, low mechanical strength, easy abrasion and the like of PTFE and heterogeneous materials on one hand, and on the other hand, the introduction of the microcapsule enables the PTFE lubricating material to have a self-repairing regulation function, enhances the antifriction and wear resistance of the material, and prolongs the service life of the lubricating material.

Description

Self-repairing self-lubricating material and preparation method thereof

Technical Field

The invention belongs to the technical field of self-lubricating composite materials, and particularly relates to a self-repairing self-lubricating material, a preparation method and application.

Background

Polytetrafluoroethylene is an important engineering plastic, and the application of PTFE has been greatly developed since the first synthesis by American scientists in 1938. The phenomena of friction and abrasion commonly exist in mechanical equipment, and the friction and abrasion cause huge energy waste and economic loss. PTFE has a very low friction factor and excellent chemical resistance and high temperature stability and is commonly used as a solid self-lubricating material. PTFE is polymerized by tetrafluoroethylene, a C-C main bond is completely wrapped by F atoms to form a streamline cylindrical structure, attractive force between rod-shaped molecules is extremely small, and the molecules can easily slide, so that a transfer film is formed on the surface of a friction part, the contact between the friction parts is shown as the contact between the transfer film and a PTFE composite material, the shear stress of a contact surface is reduced, the friction factor is reduced, and the self-lubricating effect is achieved. The tribological characteristics and excellent physicochemical properties of PTFE enable PTFE to play an important role in the field of oil-free and self-lubricating, but the special composition and structure simultaneously enable PTFE to have a plurality of defects, such as poor mechanical properties, low compatibility with other materials, easy abrasion and the like, thereby greatly limiting the wide application of PTFE in the industry. In addition, with the continuous development of industry in recent years, various severe working conditions put higher demands on the performance of the PTFE lubricating material.

In order to improve the comprehensive performance of the PTFE material, a great deal of research is carried out on the modification of PTFE by adopting methods such as filling, blending, surface modification and the like. Many types of microfillers reduce the wear rate of PTFE, and currently, graphite, carbon, fiberglass, copper, and the like are widely used as microfillers. A plurality of achievements are achieved by filling and modifying PTFE by various fillers or reinforcements. These efforts still present some problems, mainly expressed in the following two aspects: one is the interfacial adhesion problem. The interfacial adhesion between the filler or reinforcement and the matrix in the composite is poor due to the non-tackiness of the PTFE itself. Although many studies have attempted to improve the interfacial adhesion problem of composite materials by various methods, these studies have focused only on surface treatment of fillers or reinforcements, and the modification effect is limited. The second is the problem of wear. Although the introduction of filler or reinforcement in combination with PTFE improves the wear resistance to varying degrees, wear once occurring is irreversible and further research is needed to improve the service life of the material.

Disclosure of Invention

Aiming at the problems (poor adhesion, easy abrasion and the like) of PTFE-based solid self-lubricating at present, the invention firstly prepares PTFE core-shell structured nano particles and microcapsules containing a repairing agent, then prepares a block lubricating material and a film lubricating material according to a certain proportion,

a solid self-lubricating material with a self-repairing function comprises modified PTFE and a microcapsule containing a repairing agent, wherein the modified PTFE is of a core-shell structure, PTFE nano particles are used as a core, and a wear-resistant polymer or a two-dimensional material is used as a shell; the microcapsule takes a liquid repairing agent as a capsule core and takes a polymer or a two-dimensional material as a capsule wall.

Further, the wear-resistant polymer is one or more of the following materials: polymethyl methacrylate, polystyrene, acrylic resin, polyacrylamide and polyformaldehyde.

Further, the two-dimensional material is one or more of the following materials: graphene, molybdenum disulfide, hexagonal boron nitride, tungsten disulfide, titanium disulfide, molybdenum diselenide, antimony telluride, and bismuth telluride.

Further, the liquid repairing agent is one or more of the following materials: dibutyl phthalate, glycidyl methacrylate, linseed oil and tung oil.

Further, the microcapsule wall is made of one or more of the following materials: polymethyl methacrylate, polyvinylpyrrolidone, urea resin, epoxy resin, polystyrene and polyformaldehyde.

Further, the thickness of the microcapsule wall is 20nm-50 μm.

Further, in the core-shell structure of the PTFE, the thickness of the shell is 10 to 300nm, the mass fraction of the PTFE nanoparticles is 10 to 90wt%, and more preferably the mass fraction of the PTFE nanoparticles is 75 to 85 wt%.

Further, the weight of the microcapsule accounts for 0.1-70wt% of the total weight of the material, and the amount of the microcapsule accounts for 10-35 wt% of the total weight of the material.

Further, the mass of the two-dimensional material in the microcapsule accounts for 0.1-60wt% of the weight of the microcapsule, and the amount of the two-dimensional material accounts for 15-35 wt% of the weight of the microcapsule.

The preparation method of the solid self-lubricating material comprises the following steps:

(1) preparation of PTFE core-shell structure nano particles

1) Weighing a certain amount of PTFE concentrated dispersion according to the composition ratio of the PTFE core-shell structure particles, and adding deionized water to prepare PTFE dispersion A;

2) dropping a certain amount of polymer monomer into the dispersion liquid A under the mechanical stirring action of 200-1200rmp, slowly heating to 65-78 ℃, and adding 10ml of potassium persulfate (0.74mmol) solution;

3) reacting for 6-24h under nitrogen atmosphere, repeatedly centrifuging and washing after the reaction is finished, and drying for 2-12h at 80-90 ℃ to obtain the PTFE core-shell structure nano particle.

Preferably, in step 1), the mass fraction of PTFE in the core-shell structure of PTFE is from 10 to 90 wt.%, more preferably, the mass fraction of PTFE is from 75 to 85 wt.%;

preferably, in the step 1), in the core-shell structure of the PTFE, the thickness of the shell is 10-300 nm;

preferably, in step 2), the shell raw material is one or more of the following materials: polymethyl methacrylate, polystyrene, acrylic resin, polyacrylamide, polyoxymethylene, and the like.

(2) Preparing microcapsules containing a liquid repairing agent by using an in-situ polymerization method or a Pickering emulsion method, wherein the method comprises the following steps:

1) adding a certain amount of liquid repairing agent into a water solution containing a surfactant according to the composition ratio of the microcapsule, and stirring for 0.5-2h at the rotating speed of 200-1500rmp to form stable microemulsion B;

2) adding resorcinol, ammonium chloride and 1-3 drops of n-octanol defoamer into the microemulsion B, adjusting the pH to 2.5-4.5, adding a certain amount of capsule wall raw materials, slowly heating to 50-70 ℃, and reacting for 2-6 h;

3) filtering and washing after the reaction is finished, and drying for 1-3 days at normal temperature to obtain the microcapsule.

Preferably, in step 1), the microcapsule wall thickness is 20nm to 50 μm.

Preferably, in step 1), the surfactant is one or more of the following materials: gelatin, gum arabic, polyvinyl alcohol (PVA), Sodium Dodecylbenzenesulfonate (SDBS), Sodium Dodecylaminosulfate (SDS), styrene maleic acid copolymer (SMA), ethylene maleic acid copolymer (EMA), and the like.

Preferably, in step 1), the liquid repairing agent is one or more of the following materials: dibutyl phthalate, glycidyl methacrylate, linseed oil, tung oil and the like.

Preferably, in step 2), the microcapsule wall is made of one or more of the following materials: polymethyl methacrylate, polyvinylpyrrolidone, urea resin, epoxy resin, polystyrene, polyoxymethylene, and the like.

Pickering emulsion method for preparing microcapsule

1) Mixing a certain amount of two-dimensional material dispersion liquid with a liquid repairing agent according to the composition proportion of microcapsules

2) Centrifugally mixing for 4-60min at the rotating speed of 800-.

Preferably, in step 1), the two-dimensional material is one or more of the following materials: graphene, molybdenum disulfide, hexagonal boron nitride, tungsten disulfide, titanium disulfide, molybdenum diselenide, antimony telluride, bismuth telluride and the like.

Preferably, in step 1), the mass of the two-dimensional material is 0.1-60 wt.% of the weight of the microcapsules, and more preferably, the amount of the two-dimensional material is 15-35 wt.% of the weight of the microcapsules.

Preferably, in the step 2), the particle diameter of the microcapsule is 100nm-50 μm, and the capsule wall thickness is 50nm-15 μm

(3) Composite of PTFE core-shell structure nano particle and microcapsule

1) According to the composition proportion of the composite material, a certain amount of PTFE core-shell structure nano particles are mixed with the microcapsules, and the block composite material is obtained by compression molding at the temperature of 2-10MP and 100-plus-material 160 DEG C

2) According to the composition ratio of the composite material, a certain amount of PTFE core-shell structure nano particles and microcapsules are mixed in a solvent, and a composite material film is prepared by adopting a spin-coating method.

Preferably, in steps 1), 2), the amount of microcapsule is 0.1-70 wt.%, more preferably 10-35 wt.% of the total weight of the material.

The invention has the beneficial effects that: the invention provides a method for carrying out core-shell surface modification on PTFE by adopting a seed emulsion method, and introduces a microcapsule type self-repairing system into a PTFE matrix on the basis, thereby realizing the self-repairing of a lubricating material and prolonging the service life of equipment.

Drawings

FIG. 1 is an SEM image of a PTFE core-shell structure before and after modification.

FIG. 2 is a TEM image of a modified PTFE of the present invention.

FIG. 3 is an SEM image of a microcapsule of the present invention.

FIG. 4 is a photograph of the self-lubricating composite material of the present invention.

FIG. 5 is a graph of the friction coefficient of the self-repairing self-lubricating composite material of the present invention.

FIG. 6 is an optical microscope picture of the material grinding crack before and after the composite material of the present invention is repaired.

FIG. 7 is a graph showing a friction coefficient in example 2 of the present invention.

Detailed Description

The examples given below illustrate the invention in more detail. It should be noted that the following examples are only intended to illustrate the present invention and should not be construed as limiting the scope of the present invention, and that other variants and modifications of the present invention are possible to those skilled in the art on the basis of the following description, and not exhaustive enumeration of all examples. All obvious changes or modifications of the technical solution belonging to the present invention still fall within the protection scope of the present invention.

Example 1

(1) Preparation of PTFE core-shell structure particles

70 ml of PTFE dispersion were charged into a four-necked flask containing 500 ml of deionized water with stirring at 300rmp, heated to 75 ℃ and 70 ml of methyl methacrylate (0.654mol) were added. After stabilization for 30min, adding a potassium persulfate aqueous solution (10mL,0.74mmol), reacting for 20h under the nitrogen atmosphere, repeatedly centrifuging to collect a product, and drying at 85 ℃ for 5h to obtain the polymethyl methacrylate coated PTFE core-shell structure nanoparticles. The samples before and after the PTFE core-shell modification were characterized by scanning electron microscopy, and the results are shown in FIG. 1. As can be seen from FIG. 1, pure PTFE before modification has an ellipsoidal structure and after modification has a spherical structure. In order to further analyze the structure of the modified product, a transmission electron microscope is used for characterizing the modified sample, and the result is shown in fig. 2, wherein the modified particles are in a core-shell structure.

(2) Microcapsule preparation

Adding 400ml of deionized water and 0.8g of SDBS (sodium dodecyl benzene sulfonate), 0.4g of PVA-124 and stirring for 30min at the rotating speed of 400rmp into a 1L four-neck flask to obtain a surfactant aqueous solution, then sequentially adding 5g of urea, 0.5g of resorcinol and 0.5g of chlorinated polyether and two drops of n-octanol defoaming agent, adjusting the pH of the solution to 3.5 by using sodium hydroxide and acetic acid, adding 60 ml of dibutyl phthalate as a core material, stirring for 30min at the rotating speed of 400rmp to obtain a stable oil-in-water emulsion, then adding 12.67g of formaldehyde solution with the mass fraction of 37% to initiate polycondensation reaction, slowly heating the solution to 55 ℃, preserving heat for 4h to finish the reaction, cooling, carrying out suction filtration and drying on the reaction solution to obtain microcapsule powder with the urea formaldehyde resin as the capsule wall and the dibutyl phthalate as the capsule core. The microcapsules were characterized by scanning electron microscopy, and as can be seen from FIG. 3, the microcapsules had a particle size of about 1.5 μm and a wall thickness of about 100 nm.

(3) Preparation of self-repairing self-lubricating composite material

0.6g of PTFE core-shell structure particles and 0.4g of microcapsules are mixed, and the mixture is subjected to compression molding at 6MP and 140 ℃ to obtain a block composite material, as shown in figure 4.

(4) Composite material friction and self-repairing performance test

The composite material was tested on a UMT-5 friction and wear testing machine, and the change of the friction coefficient is shown in FIG. 5, and the results show that the friction coefficient of the composite material is greatly reduced compared with that of a pure PTFE sample. The wear scar of the tested sample is analyzed, and the self-repairing of the wear scar is realized after the sample is heated for 5 hours at 50 ℃ according to an optical microscope picture, as shown in figure 6.

Example 2

(1) Preparation of PTFE core-shell structure particles

70 ml of PTFE dispersion were charged into a four-necked flask containing 400ml of deionized water with stirring at 400rmp, heated to 70 ℃ and 35 ml of methyl methacrylate were added. After stabilization for 30min, adding a potassium persulfate aqueous solution (10mL,0.37mmol), reacting for 24h under a nitrogen atmosphere, repeatedly centrifuging to collect a product, and drying at 80 ℃ for 8h to obtain the polymethyl methacrylate coated PTFE core-shell structure particles.

(2) Microcapsule preparation

10ml of graphene oxide dispersion liquid is mixed with 0.8g of linseed oil, the mixture is mixed for 15 minutes under the action of high shear of 900 revolutions to prepare pickering emulsion, and the pickering emulsion is dried for 10 hours at normal temperature to obtain the microcapsule.

(3) Preparation of self-repairing self-lubricating composite film

A certain amount of PTFE core-shell structure particles and microcapsules are mixed in a solvent, and a composite material film is prepared by adopting a spin-coating method.

(4) Composite material friction and self-repairing performance test

The composite material was tested on a UMT-5 friction abrasion tester, and the change in coefficient of friction is shown in FIG. 7.

The above embodiments describe the technical solutions of the present invention in detail. It will be clear that the invention is not limited to the described embodiments. Based on the embodiments of the present invention, those skilled in the art can make various changes, but any changes equivalent or similar to the present invention are within the protection scope of the present invention.

Claims

1. The preparation method of the solid self-lubricating material with the self-repairing function is characterized in that the solid self-lubricating material comprises modified PTFE and a microcapsule containing a repairing agent, wherein the modified PTFE is core-shell structure particles, the PTFE particles are taken as a core, and a wear-resistant polymer or a two-dimensional material is taken as a shell; the microcapsule takes a liquid repairing agent as a capsule core and takes a polymer or a two-dimensional material as a capsule wall; the liquid repairing agent is dibutyl phthalate; the wear-resistant polymer is one or more of the following materials: polymethyl methacrylate, polystyrene, acrylic resin, polyacrylamide and polyformaldehyde; the two-dimensional material is one or more of the following materials: graphene, molybdenum disulfide, hexagonal boron nitride, tungsten disulfide, titanium disulfide, molybdenum diselenide, antimony telluride, and bismuth telluride;

the preparation method comprises the following steps:

(1) preparing a core-shell structure with PTFE as a core, comprising:

1) adding the PTFE concentrated dispersion liquid into deionized water to prepare PTFE dispersion liquid A;

2) dropwise adding a shell raw material into the dispersion liquid A under the stirring condition, slowly heating, and adding a potassium persulfate solution;

3) centrifuging, washing and drying after the reaction is finished to obtain a PTFE core-shell structure;

(2) preparing microcapsules containing a liquid repairing agent by an in-situ polymerization method, wherein the microcapsules comprise:

1) adding a liquid repairing agent into an aqueous solution containing a surfactant, mixing and stirring to form a microemulsion B;

2) adding a defoaming agent into the microemulsion B, adding a capsule wall raw material, and heating for reaction;

3) after the reaction is finished, filtering, washing and drying to obtain microcapsules;

(2') or preparing the microcapsule containing the liquid repairing agent by using a Pickering emulsion method, comprising the following steps:

1) mixing the two-dimensional material dispersion liquid with a liquid repairing agent;

2) centrifuging the mixed solution obtained in the step 1), filtering and drying to obtain microcapsules;

(3) the self-lubricating material with the self-repairing function is prepared by compounding a PTFE core-shell structure and a microcapsule, and comprises the following steps:

1) mixing the PTFE core-shell structure particles with the microcapsules, and carrying out compression molding at the temperature of between 2 and 10MPa and between 100 and 160 ℃ to obtain a block composite material;

2) and mixing the PTFE core-shell structure particles and the microcapsules in a solvent, and preparing the composite material film by adopting a spin-coating method.

2. The preparation method according to claim 1, wherein the microcapsule wall is one or more of the following materials: polymethyl methacrylate, polyvinylpyrrolidone, urea resin, epoxy resin, polystyrene and polyformaldehyde.

3. The method for preparing the microcapsule according to claim 1, wherein the microcapsule wall thickness is 20nm to 50 μm.

4. The preparation method according to claim 1, wherein in the PTFE core-shell structure, the thickness of the shell is 10-300nm, and the mass fraction of the PTFE particles is 10-90 wt%.

5. The preparation method according to claim 1, wherein the mass of the microcapsule is 0.1 to 70wt% based on the total weight of the material.

6. The method of claim 1, wherein the microcapsules are present in an amount of 10-35 wt.% based on the total weight of the material.

7. The method according to claim 1, wherein the mass of the two-dimensional material in the microcapsule is 0.1 to 60wt% based on the weight of the microcapsule.